This invention relates in general to handling, testing and sorting apparatus for electronic devices. More specifically, it relates to apparatus that repeatedly drives two parallel sets of contacts into electrical connection with corresponding leads on an integrated circuit in a symmetrical manner.
In the manufacture of integrated circuits (IC's) and the like, it is important to test each IC reliably and at a high throughput rate. Typically modern IC handler/testers operate at rates in excess of 5,000 IC'per hour with each IC being held at a test site for testing that is completed in a time interval of typically 100 milliseconds. Once an IC comes to rest at the test site, its leads are connected to test circuitry by a set of contacts. IC's generally have a rectilinear, box-like body with two parallel rows of leads originating from the sides of the body, curving rapidly at a shoulder, and then extending in a direction generally normal to one face of the body. The contacts are arrayed in two parallel rows with the IC positioned between the contacts so that one contact or a pair of contacts can make an electrical connection with a corresponding lead on the IC.
Although the contacts can be mounted on a movable member that carries them into and out of electrical connection, as described in commonly assigned U.S. Pat. No. 4,047,780, they are more commonly mounted with one end fixed. The free end makes the electrical connection. The contacts are normally spaced from the leads, but the spacing is close enough that they can be flexed into connection by a driving member. The most common driving arrangement is to use two separate drive elements, such as solenoids, that each propel a rigid member against one of the rows of contacts causing it to flex.
In order to have a reliable test, each contact should make a good electrical connection with its associated lead. Because some leads may be out of alignment, it is therefore important that the contacts flex far enough to make a reliable connection with every lead. Flexure distance can also be important where the size of the IC's being tested vary or the angular orientation and therefore the position of the leads with respect to the IC's body vary. Reliability is also a function of the uniformity and magnitude of the contact force. Clearly an increased stroke of a drive element will flex the contacts more and produce an increased contact force. A countervailing consideration is that repeated large flexures of the contacts results in metal fatigue that can deteriorate the resilience of the contact to a level where it adversely affects the reliability of the test.
The contact system must also operate on IC's of different sizes. Usually a wide variation in the width being tested will require a change in the contact assembly. The drive assembly for the contacts, however, is a normally fixed component of the testing apparatus. The drive assembly remains in position and must be adjustable.
It is also significant that the IC's are normally loosely-guided to facilitate their movement through the tester and to accommodate variations in size. This is true at the test site also. However, if one set of contacts is driven into connection with one row of leads before the other set reaches its leads, then the drive system will push the entire IC to one side. This is undesirable because it varies the contact force on the leads and results in a less reliable test. It also can accentuate the metal fatigue problem discussed above because one set of contacts flexes through a greater distance to establish the desired contact force. Ideally then, all the contacts should make physical contact with the leads at substantially the same time. The aforementioned U.S. Pat. No. 4,047,780 describes a scotch yoke drive that produces a symmetrical clamping movement of two sets of contacts. An important consideration in the '780 patent is to develop this motion in a narrow space (measured in the direction of the leads) to minimize the separations between the device being tested and the test circuitry. While the '780 contact drive works well, it is a comparatively complex structure with attendant cost disadvantages. Also, its geometry places limitations on its usefulness.
It is therefore a principal object of this invention to provide a simple contact drive system that produces a symmetrical drive force on two parallel rows of contacts that develop a uniform contact force and minimizes movement of the IC as it is connected to the contacts.
Another object is to provide a contact drive system with the foregoing advantages that is readily adjusted to accommodate different IC's or to vary the operation of the contact system.
A further object is to provide a contact drive system with the foregoing advantages that has a comparatively low cost of manufacture and is rugged and reliable in operation.
Another object is to provide a contact drive system with the foregoing advantages that is spatially compact, particularly in the lateral direction, to allow a high density, parallel processing of IC's.